1. Field of the Invention
The present invention relates to a flameproof housing, and more particularly, to a flameproof housing with a display.
2. Statement of the Problem
Vibrating conduit sensors, such as Coriolis mass flowmeters and vibrating densitometers, typically operate by detecting motion of a vibrating conduit that contains a flowing material. Properties associated with the material in the conduit, such as mass flow, density and the like, can be determined by processing measurement signals received from motion transducers associated with the conduit. The vibration modes of the vibrating material-filled system generally are affected by the combined mass, stiffness and damping characteristics of the containing conduit and the material contained therein.
A typical Coriolis mass flowmeter includes one or more conduits that are connected inline in a pipeline or other transport system and convey material, e.g., fluids, slurries, emulsions, and the like, in the system. Each conduit may be viewed as having a set of natural vibration modes, including for example, simple bending, torsional, radial, and coupled modes. In a typical Coriolis mass flow measurement application, a conduit is excited in one or more vibration modes as a material flows through the conduit, and motion of the conduit is measured at points spaced along the conduit. Excitation is typically provided by an actuator, e.g., an electromechanical device, such as a voice coil-type driver, that perturbs the conduit in a periodic fashion. Mass flow rate may be determined by measuring time delay or phase differences between motions at the transducer locations. Two such transducers (or pickoff sensors) are typically employed in order to measure a vibrational response of the flow conduit or conduits, and are typically located at positions upstream and downstream of the actuator. The two pickoff sensors are connected to electronic instrumentation. The instrumentation receives signals from the two pickoff sensors and processes the signals in order to derive a mass flow rate measurement, among other things. Vibratory flowmeters, including Coriolis mass flowmeters and densitometers, therefore employ one or more flow tubes that are vibrated in order to measure a fluid.
In some environments, electrical signals may need to be conducted through a flameproof physical barrier or housing. For example, a housing may surround and enclose electrical circuits of a meter electronics or transmitter. Process control transmitters designed for use in hazardous atmospheres often utilize a combination of protection methods, including flameproof housings and/or barriers, to avoid uncontrolled explosions of flammable gases. International standards define the compliance requirements for flameproof devices and structures.
In the case of Coriolis flowmeter transmitters, it is well known to enclose the active electronics components within a flameproof compartment or housing so that an explosion of gases that might occur as a result of electrical energy within the electronics will not propagate beyond the enclosure. Consequently, the housing is desired to be sealed off, including display components that need to remain externally visible.
FIG. 1 shows a prior art flameproof display panel interface using a prior art curable sealing material. A potting material or adhesive is applied to one or both of the housing and/or the glass panel before assembly and comprises a curable sealing material. When the glass panel is moved into position in the housing, as shown, the potting material or adhesive is at least partially compressed between the glass panel and a portion of the housing. The potting material or adhesive therefore is desirably spread over essentially an entire interface region between the glass panel and the corresponding portion of the housing. The curable sealing material may then cure over time, or may be subject to heating or other processes to cure the material. The potting material or adhesive not only may seal the glass panel to the housing, but may also bond the two components together, thereby providing a cementing function.
The prior art has drawbacks. The potting material or adhesive may be subject to environmental and/or workplace regulations and may therefore be expensive and costly to handle, to apply, and to dispose of. The potting material or adhesive may not be allowed by regulation in some locales. The potting material or adhesive can be improperly or incompletely applied. After installation, the potting material or adhesive may include air bubbles, cracks, furrows, or irregular boundaries or may be too narrow to form a flame path of a desired length. The potting material or adhesive may shrink and/or crack with age, wherein the glass panel may exhibit leakage over time. The potting material or adhesive may lose adhesion to one or both of the glass panel and the housing.
What is needed, therefore, is a glass display panel that does not require cementing in order to achieve a flameproof seal with a corresponding housing.